Actions Runner Controller 0.15.0 [GA]

### Value Prop
Actions Runner Controller (ARC) 0.15.0 makes it easier to configure, operate, and troubleshoot self-hosted runners on Kubernetes — with cleaner Helm chart configuration, improved logging, and a batch of fixes and improvements requested directly by the ARC community. Platform teams spend less time wrestling with rough edges and more time shipping. This release incorporates vetted community contributions, so the improvements reflect real-world usage at scale.

### Expected Outcome
Teams running GitHub Actions on Kubernetes gain a more stable and polished ARC experience, with fewer day-to-day friction points and better visibility when things go wrong. By consistently addressing community-reported issues and merging community pull requests, this release builds confidence in the ARC release cadence and migration path away from legacy ARC.

此路线图 issue 涵盖面向 Kubernetes 上 GitHub Actions 的 Actions Runner Controller 0.15.0 版本发布。首先确定版本发布范围，包括 Helm chart 配置、日志记录、修复和社区贡献；payload 未指定任何文件、测试或入口点。完成标准是交付所述的版本发布改进，并验证预期的稳定性和故障排查结果。

由索引模型根据 Issue 内容生成。